<!DOCTYPE html>
<html lang="en">

<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <meta http-equiv="X-UA-Compatible" content="ie=edge">
    <title>Document</title>
    <script src="./lib/vue.min-2.6.11.js"></script>
</head>

<body>
    <div id="app">
        <input type="text" v-model='n1'>

        <select v-model="opt">
            <option value="+">+</option>
            <option value="-">-</option>
            <option value="*">*</option>
            <option value="/">/</option>
        </select>
        <input type="text" v-model='n2'>
        <input type="button" value="=" @click="calc">
        <input type="text" v-model="result">
    </div>
</body>
<script>

    const vm = new Vue({
        el: '#app',
        data: {
            n1: 0,
            n2: 0,
            opt: '+',
            result: 0
        },
        methods: {
            // 计算结果
            calc() {

                // if (this.opt == '+') {
                //     this.result = Number(this.n1) + Number(this.n2)
                // }
                switch (this.opt) {
                    case '+':
                        this.result = Number(this.n1) + Number(this.n2)
                        // parseFloat(this.n1) + parseFloat(this.n2)
                        // Number(this.n1) + Number(this.n2)
                        break;
                    case '-':
                        this.result = Number(this.n1) - Number(this.n2)
                        break;
                    case '*':
                        this.result = Number(this.n1) * Number(this.n2)
                        break;
                    case '/':
                        this.result = Number(this.n1) / Number(this.n2)
                        break;
                    default:
                        break;
                }

                // ***不建议的写法***， 将字符串转换成 代码 并执行
                // const str = Number(this.n1) + this.opt +  Number(this.n2)
                // this.result = eval(str)

            }
        }
    })






</script>

</html>